Transdermal delivery of a therapeutically active agent through the skin provides a means for a sustained, constant plasma level of the agent. It differs from conventional therapy via oral administration in that blood levels remain constant throughout the period during which the transdermal system is on the skin, providing a blood concentration of drug without the peaks and troughs of drug concentration seen in oral delivery. Transdermal delivery is utilized for drugs with a short half-life and/or when there is a significant first-pass effect of the liver that can prematurely metabolizes the drug than long half drugs.
Oral administration of drugs with a long elimination half-life can achieve a relatively constant blood level of drugs with the minimal peaks and valleys within the therapeutic range at the steady state for long half-life drugs. Oral administration of a long half-life drug (not less than 48 hours) brings about accumulation of the drug in the blood over time until it reaches the steady state blood level in the therapeutic range.
It would be desirable to take advantage of the long half-lives of drugs in designing a transdermal delivery system which is therapeutically equivalent to the oral dosage route with respect to the pharmacokinetic parameters of area under the curve (AUC) and maximum blood concentration (Cmax). The achievement of bioequivalence can reduce extensive non-clinical and clinical test costs.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.